This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2011/051310, filed on Jan. 31, 2011, the disclosure of which is incorporated herein by reference in its entirety.
The disclosure relates to an internal gear pump for a hydraulic vehicle braking system having the features of the disclosure. Such internal gear pumps are used, instead of the piston pumps usually employed, in slip-controlled and/or externally powered vehicle braking systems and are often referred to, if not necessarily accurately, as return pumps.
Internal gear pumps are known. They comprise a pinion, that is, an externally toothed gear wheel, which is arranged in an internally toothed ring gear with which it meshes at a point on the circumference, or in a circumferential section. Through rotational driving of the pinion the ring gear is also driven in rotation and the internal gear pump delivers fluid in known fashion; in a hydraulic vehicle braking system it delivers brake fluid.
Opposite the circumferential section in which the pinion meshes with the ring gear, the internal gear pump has a crescent-shaped cavity between the pinion and the ring gear in which a filler piece is arranged.
The filler piece is normally pivoted about an axis parallel to the axis of the internal gear pump. Because of its curved shape, the filler piece is also referred to as a sickle, and internal gear pumps having such a filler piece are also referred to as sickle pumps. Tooth heads of the pinion bear against a concave inner side of the filler piece and tooth heads of the ring gear against a convex outer side of the filler piece. When the gear pump is driven, the tooth heads of the pinion and of the ring gear slide along the inner and outer sides of the filler piece respectively. The filler piece seals gaps between the pinion teeth and between the ring gear teeth along the circumference, so that fluid volumes are enclosed in the gaps between the teeth of the pinion and of the ring gear and are delivered by the rotational driving of the pinion and the ring gear from a pump inlet to a pump outlet. The pump inlet forms a suction side and the pump outlet a pressure side of the internal gear pump.
The patent DE 196 13 833 B4 discloses such an internal gear pump, the filler piece of which is divided in the circumferential direction and comprises an inner part referred to as the segment carrier and are outer part referred to as the segment. Leaf springs arranged between the inner part and the outer part press the inner part and the outer part radially apart and against the tooth heads of the pinion and of the ring gear in order to achieve a good abutment against the tooth heads and therefore a good sealing effect, which is a prerequisite for high efficiency of the internal gear pump. When the internal gear pump builds up a pressure during operation, this pressure acts on a gap or intervening space between the inner part and the outer part in a pressure-side region of the filler piece. In a central region an intermediate pressure acts on the intervening space between the inner part and the outer part, and in a suction-side region the suction pressure of the internal gear pump prevails in the intervening space between the inner part and the outer part. The pressure build-up during operation of the internal gear pump presses the inner part and the outer part of the filler piece of the known internal gear pump apart and against the tooth heads of the pinion and of the ring gear, additionally to the leaf springs, in order to improve the sealing effect.
The leaf springs arranged between the inner part and the outer part of the filler piece of the known internal gear pump are disposed transversely to the filler piece, that is, parallel to an axis of the internal gear pump. In order to achieve a significant spring travel, the springs must have a certain length, which determines a minimum width of the internal gear pump.